(Swift + Firebase) Convert observeSingleEvent to observe .childAdded - ios

Question

I have a observeSingleEvent in my viewDidLoad function and I want to change it into a observe with .childAdded so that it will listen constantly and add the objects whenever they get added to the database.
Here's the code that reads from firebase:
let parentRef = Database.database().reference().child("Recipes")
parentRef.observeSingleEvent(of: .value, with: { snapshot in
// PROCESSES VALUES RECEIVED FROM SERVER
if ( snapshot.value is NSNull ) {
// DATA WAS NOT FOUND
print("– – – Data was not found – – –")
} else {
// DATA WAS FOUND
for user_child in (snapshot.children) {
let user_snap = user_child as! DataSnapshot
let dict = user_snap.value as! [String: String?]
// DEFINE VARIABLES FOR LABELS
let recipeName = dict["Name"] as? String
let recipeDescription = dict["Description"] as? String
food.append(Element(name: recipeName!, description: recipeDescription!))
self.tableView.reloadData()
}
}
})
Another problem that I have now (besides that it only loads once) is that whenever I go to another view in the app and then come back it reads everything again so I get duplicates of everything in my tableView, will that still happen with the observe?
Edit:
Here is what my database looks like:
Recipes
-Kv7FAqgLtDrRoyGd-99
Description: "food description"
Name: "food name"
-KvBuzMUnIQXn8gpG2WL
Description: "food description2"
Name: "food name2"
-KvH6yYeJaThK7oP8xBj
Description: "food description3"
Name: "food name3"

Answer 1

Change observeSingleEvent to observe.
Empty food array whenever observing new values.
Reload your food array outside your for-loop so that you only reload whenever you have loaded all of your items into your array.
let parentRef = Database.database().reference().child("Recipes")
// 1. Change to observe
parentRef.observe(.value, with: { snapshot in
// PROCESSES VALUES RECEIVED FROM SERVER
if ( snapshot.value is NSNull ) {
// DATA WAS NOT FOUND
print("– – – Data was not found – – –")
} else {
// 2. Empty food array
self.food = []
// DATA WAS FOUND
for user_child in (snapshot.children) {
let user_snap = user_child as! DataSnapshot
let dict = user_snap.value as! [String: String?]
// DEFINE VARIABLES FOR LABELS
let recipeName = dict["Name"] as? String
let recipeDescription = dict["Description"] as? String
food.append(Element(name: recipeName!, description: recipeDescription!))
}
// 3. reload tableview outside loop
self.tableView.reloadData()
}
})
By emptying your food array whenever observing new values you ensure to only show the values that are present in your database and thus never having repetitive elements.